Preparation Of Co-N Co-doped Carbon Catalysts And Their Application In The Catalytic Hydrogenation Of Nitrobenzene

Aniline and its derivatives are an important class of compounds in the production of chemical industry.The most widely used production method is the catalytic hydrogenation of nitrobenzene.The use of hydrogen molecules for liquid phase catalysis of nitrobenzene is a reasonable choice.Precious metal catalysts（such as Pt,Pd,Rh,Ru,etc.）have been extensively studied in the past few decades,but they have shortcomings such as low reserves,high cost,and easy deactivation.Therefore,it is very important to develop a non-precious catalyst with higher activity.Cobalt,a non-precious metal,has attracted widespread attention because of its low cost and easy availability and good activity in various catalytic applications.The support also plays a vital role in the activity of the catalyst.Among the many supports,nitrogen-doped carbon materials have a special chemical structure on the surface and can promote the catalytic activity and stability of the catalyst.It is a type of support that has been studied in recent years.In this paper,Co-N co-doped porous carbon materials were synthesized by in-situ method with ZIF-67 as sacrificial template,one-pot method with glucose as carbon source,urea as nitrogen source,cobalt nitrate as metal source and semi-polymerized glucose modified ZIF-67 complex by in-situ pyrolysis,and used for catalytic nitrobenzene hydrogenation test.The main contents are summarized as follows:Firstly,several Co-N co-doped porous carbon materials were prepared by in-situ carbonization of ZIF-67.By adjusting the molar ratio of 2-methylimidazole and Co²⁺（4,6,8 and 10）required for the synthesis of ZIF-67,ZIF-67 of different sizes was obtained,and then one-step high temperature pyrolysis at 900℃ to obtain ZIF-67 basic morphology of N-doped carbon-supported Co catalysts and used them for nitrobenzene catalytic hydrogenation test.The results showed that the carbonization of ZIF-67synthesized with a molar ratio of 2-methylimidazole and Co²⁺of 8 to obtain Co@NCZ-8 at 100℃ and 1 MPa H₂ for 3 h can achieve 100%conversion of nitrobenzene,and Aniline is the only product.And in the first 6 cycles,the conversion rate of nitrobenzene is maintained above 80%,and the selectivity of aniline is>99%.Second,we synthesized Co-N co-doped porous carbon material using biomass glucose as the carbon source.Glucose hydrothermal carbon was prepared by adding a certain amount of Zn Cl₂ as a catalyst during the hydrothermal carbonization of glucose.The hydrothermal carbon was mixed with different proportions of Co（NO₃）₂·6H₂O and urea and then carbonized at 600-900℃ to obtain Co-N co-doped carbon catalyst.The results show that the catalyst obtained by this method retains the spherical morphology of glucose hydrothermal carbon.Through its catalytic performance test,it is found that the carbonized sample 10%Co@NCG-800 at 800℃ has the best catalytic effect,which can completely convert nitrobenzene into aniline within 3 h at 100℃ and 1 MPa H₂pressure.Finally,we combined the glucose semi-polymer obtained by low-temperature hydrothermal carbonization with ZIF-67 to synthesize Co-N co-doped porous carbon material.Glucose was mixed into ZIF-67 in situ after hydrothermal at 160℃ to obtain composite spheres with lamellar morphology.And when the molar ratio of MIM to glucose is 2 and carbonized at 800℃,the resulting Co@NCZG-2 has a maximum specific surface area of 406 m²/g.This type of material is used in the test of nitrobenzene catalytic hydrogenation,where Co@NCZG-2 can reach a nitrobenzene conversion rate of 100%at 80℃ and 1 MPa H₂ for 90 min,and the selectivity of aniline up to 99%.